In the processing of high molecular weight elastomer compositions, it has become standard to employ plasticizers in order to decrease the viscosity and thereby to improve the workability of the composition. In general, extender oils such as mineral oils or paraffinic oils have been employed to plasticize rubber compounds.
However, the incorporation of such oils into the rubber composition, while effectively plasticizing such composition, will produce a number of deleterious effects upon the cured composition. Among these undesirable effects are decreased tensile strength, poor resistance to extraction and poor low temperature flexibility.
U.S. Pat. No. 3,819,592 to Visser at al discloses a process for producing liquid ethylene/propylene/(optionally) nonconjugated diene copolymers employing a vanadium salt-alkylaluminum halide catalyst and a molecular weight regulator which is a phosphorodithioate, a dithiocarbamate or a dithiocarbonate. This patent broadly discloses that curable liquid ethylene/alphaolefin/diene terpolymers can be utilized as adhesives, caulking compounds, sealants and plasticizing coagulants. However, Visser et al neither discloses any actual formulations nor provides any incentive in so employing such compounds.
It is elementary polymer chemistry that low molecular weight polymers will, upon curing, possess reduced tensile strength relative to higher molecular weight polymers. Consequently, the finding that the compositions of this invention, which comprise a blend of high and low molecular weight polymers, will exhibit increased tensile strength relative to compositions comprising high molecular weight polymer alone which has been plasticized with equivalent amounts of conventional extender oil is completely unexpected.
Accordingly, it is an object of this invention to provide an easily processable elastomer composition which, upon curing, exhibits unexpectedly high tensile strength.
It is a further object of this invention to provide an elastomer composition which, upon curing, exhibits unexpectedly desirable resistance to ozone and extraction.
It is yet another object of this invention to provide a process for compounding a high molecular weight elastomer such that the composition containing said elastomer will be easily processable and, upon curing, will exhibit unexpectedly desirable tensile strength, ozone resistance and resistance to extraction.
The above objects and other additional objects will become more fully apparent from the following description and accompanying Examples.